Tools › Reliability › Growth and Testing › Reliability Growth › Example

MIL-HDBK-189C Table VII: Crow-AMSAA fit to grouped aircraft failure counts

ToolReliability Growth
SourceU.S. Department of Defense (2011). Reliability Growth Management. MIL-HDBK-189C, 14 June 2011. Section 6.2.3.2, Tables VII and VIII (also MIL-HDBK-189, 1981, Section 20.2.3.3).
LevelProfessional

Problem

An aircraft system was inspected after 20, 40, 60, 80 and 100 flight hours and 13, 16, 5, 8 and 7 failures were found in the five intervals. Fit the Crow-AMSAA model to the grouped data, compare the expected failures per interval with the observed by a chi-square test, and give the MTBF at 100 hours.

Inputs to Enter

  • Data format grouped (loads the example): 0 20 13 / 20 40 16 / 40 60 5 / 60 80 8 / 80 100 7
  • Goodness-of-fit significance 0.05
Open the Reliability Growth tool

Answers

  • F = 49; β = 0.753, λ = 1.53; expected failures 14.59, 9.99, 8.77, 8.07, 7.58
  • χ² = 5.5 (5.4 in the 1981 text) on 3 degrees of freedom against 7.8 at 0.05: fit accepted
  • Last-interval MTBF M_K = 20/7.58 = 2.6 flight hours, intensity 0.379; instantaneous intensity at 100 h 0.369, MTBF 2.7 hours

Notes

Choose the grouped format in the Data Format select; it fills the five interval lines.

More Examples for This Tool